Significance of peridotite samples from the oceanic core complex: role of melt on mantle heterogeneity beneath mid-ocean ridge

2013 ◽  
Vol 42 (5) ◽  
pp. 221-231 ◽  
Author(s):  
Akihiro TAMURA ◽  
Tomoaki MORISHITA ◽  
Shoji ARAI
Keyword(s):  
Mantle Heterogeneity ◽  
Core Complex ◽  
Oceanic Core Complex ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

scholarly journals Oceanic Core Complex or not? When partial spreading asymmetry triggers seafloor diversity

2021 ◽  
Author(s):  
Florent Szitkar ◽  
Laurent Gernigon ◽  
Anna Lim ◽  
Marco Brönner
Keyword(s):  
Magnetic Data ◽  
Core Complex ◽  
Oceanic Core Complex ◽  
New Class ◽  
Mid Ocean Ridge ◽  
Slow Spreading ◽  
Loki’S Castle ◽  
Definition Of ◽  
Ocean Ridge ◽  
Oceanic Structure

Abstract We use high-resolution and regional geophysical data to study a bathymetric high near the Mohns/Knipovich ridges junction, in the Norwegian-Greenland Sea. Near-seafloor magnetic data over hydrothermal site Loki’s Castle first support the basaltic nature of the seafloor. We then combine this result with regional magnetic and bathymetric considerations to investigate the crustal architecture in the vicinity of the junction. We show that the spreading asymmetry is insufficient to allow the development of Oceanic Core Complexes. Instead, this atypical off-axis hill is dominantly basaltic and should be interpreted as the first inside corner hogback structure identified along an active mid-ocean ridge system. Our conclusion tempers the definition of Oceanic Core Complex and underlines that bathymetric highs located off axis from slow-spreading centers cannot always be interpreted as such. This intermediate type of spreading paves the way to the introduction of a new class of oceanic structure referred to as Proto-Core Complexes.

scholarly journals A subduction influence on ocean ridge basalts outside the Pacific subduction shield

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
A. Y. Yang ◽  
C. H. Langmuir ◽  
Y. Cai ◽  
P. Michael ◽  
S. L. Goldstein ◽  
...  
Keyword(s):  
Upper Mantle ◽  
The Arctic ◽  
Mantle Flow ◽  
Mantle Heterogeneity ◽  
Gakkel Ridge ◽  
The Pacific ◽  
Mid Ocean Ridge ◽  
The Pacific Ocean ◽  
Back Arc ◽  
Ocean Ridge

AbstractThe plate tectonic cycle produces chemically distinct mid-ocean ridge basalts and arc volcanics, with the latter enriched in elements such as Ba, Rb, Th, Sr and Pb and depleted in Nb owing to the water-rich flux from the subducted slab. Basalts from back-arc basins, with intermediate compositions, show that such a slab flux can be transported behind the volcanic front of the arc and incorporated into mantle flow. Hence it is puzzling why melts of subduction-modified mantle have rarely been recognized in mid-ocean ridge basalts. Here we report the first mid-ocean ridge basalt samples with distinct arc signatures, akin to back-arc basin basalts, from the Arctic Gakkel Ridge. A new high precision dataset for 576 Gakkel samples suggests a pervasive subduction influence in this region. This influence can also be identified in Atlantic and Indian mid-ocean ridge basalts but is nearly absent in Pacific mid-ocean ridge basalts. Such a hemispheric-scale upper mantle heterogeneity reflects subduction modification of the asthenospheric mantle which is incorporated into mantle flow, and whose geographical distribution is controlled dominantly by a “subduction shield” that has surrounded the Pacific Ocean for 180 Myr. Simple modeling suggests that a slab flux equivalent to ~13% of the output at arcs is incorporated into the convecting upper mantle.

New  podiform chromitites Occurrence from the Masirah Ophiolite, Oman

2021 ◽  
Author(s):  
Sobhi Nasir
Keyword(s):  
Tectonic Setting ◽  
Shear Bands ◽  
Mineral Inclusions ◽  
Silicate Inclusions ◽  
Mid Ocean Ridge ◽  
Early Paleocene ◽  
Podiform Chromitites ◽  
Ocean Ridge ◽  
Mantle Section

<p>The Masirah ophiolite is one of the few true ocean ridge ophiolites that have been preserved (Rollinson, 2017) and lacks any indication that it formed in a subduction environment. The Masirah ophiolite in south-eastern Oman is a different and older ophiolite from the more famous northern Oman ophiolite. Chromite and copper ores comprise large deposits in the Samail ophiolite, northern Oman. In comparison, chromite and copper deposits have not been described in previous reports or previous exploration in Masirah ophiolite. Rollinson (2017) has proposed that the apparent absence of chromitites in the mantle section of Masirah ophiolite is an important discriminant between subduction related and ocean ridge ophiolites.  However, during recent studies on the Batain ophiolite mélange, and Masirah ophiolite, several chromitite pods have been discovered. The chromitites occur as separated small concordant, lenticular pods (3–10 m in thickness), which have been extensively altered and deformed, with the host pyroxenite serpentinites serpentinized harzburgites and dunites. The largest chromitite pods found within the pyroxenite and dunite of Masirah are up to 10 m across.  Unusual minerals and mineral inclusions (orthopyroxene, clinopyroxene, amphibole, phlogopite, serpentine, native Fe, FeO, alloy, sulfide, calcite, laurite, celestine and halite) within chromite have been observed in the chromitites from the  Masirah ophiolites.  The existence of hydrous silicate inclusions in the chromite calls for a role of hydration during chromite genesis. Both  phlogopite and hornblende were possibly formed from alkali-rich hydrous fluids/melts trapped within the chromite during the chromitite formation. High-T green hornblende and phlogopite included in the chromites is evidence of the introduction of water in the magma at the end of the chromite crystallization. Such paragenesis points to the presence of hydrous fluids during the activity of the shear bands. The chromitites parental magmas are rich in K, Na, LREE, B, Cs, Pb, Sr, Li, Rb and U relative to HREE, reflecting the alkalic fluids/melts that prevailed during the chromitites genesis.</p><p>The mineral inclusions  in association with host peridotites may have been brought by the uprising asthenosphere at mid-oceanic ridges due to the mantle convection. It appears that this chromite has been formed through reaction between amid-ocean-ridge basalt-melt with depleted harzburgite in the uppermost mantle.  The chromitite deposits have similar cr# (55-62% Al-chromitites), mg# Al2O3 and TiO2 contents to spinels found in MORB, and have been interpreted as having formed in amid-ocean ridge setting.  This suggests that this chromitites is residual from lower degree, partial melting of peridotite, which produced low-Cr# chromitites at the Moho transition zone, possibly in a mid-ocean-ridge setting. The chemistry of both mineral inclusions and chromite   suggests MORB-related tectonic setting for the chromitites that were crystallized at 1000 °C–1300 °C under pressures <3 GPa . The host peridotites were generated during the proto-Indian Ocean MORB extension and emplaced as a result of the obduction of the ophiolite over the Oman Continental margin during Late Cretaceous-Early Paleocene.</p><p>Rollinson, H., 2017. Geoscience Frontiers, 8: 1253–1262.</p>

Experimental investigation of the stability of clinopyroxene in mid-ocean ridge basalts: The role of Cr and Ca/Al

Lithos ◽  
2017 ◽  
Vol 274-275 ◽  
pp. 240-253 ◽  
Author(s):  
Martin Voigt ◽  
Laurence A. Coogan ◽  
Anette von der Handt
Keyword(s):  
Experimental Investigation ◽  
Mid Ocean Ridge ◽  
The Stability ◽  
Ocean Ridge

scholarly journals Extreme mantle heterogeneity in mid‐ocean ridge mantle revealed in lavas from the 8°20' N near‐axis seamount chain

2020 ◽  
Author(s):  
Molly Anderson ◽  
V. Dorsey Wanless ◽  
Michael Perfit ◽  
Ethan Conrad ◽  
Patricia Gregg ◽  
...  
Keyword(s):  
Mantle Heterogeneity ◽  
Mid Ocean Ridge ◽  
Seamount Chain ◽  
Ocean Ridge

scholarly journals Fractional crystallization causes the iron isotope contrast between mid-ocean ridge basalts and abyssal peridotites

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Yanhong Chen ◽  
Yaoling Niu ◽  
Meng Duan ◽  
Hongmei Gong ◽  
Pengyuan Guo
Keyword(s):  
Fractional Crystallization ◽  
Trace Element Geochemistry ◽  
Iron Isotope ◽  
Element Geochemistry ◽  
Mid Ocean Ridge ◽  
Atlantis Bank ◽  
The Indian Ocean ◽  
Ocean Ridge ◽  
Melt Evolution

AbstractThe iron isotope contrast between mid-ocean ridge basalts and abyssal peridotites is far greater than can be explained by mantle melting alone. Here we investigate a suite of mid-ocean ridge magma chamber rocks sampled by the Ocean Drilling Project Hole 735B in the Atlantis Bank of the Indian Ocean. We report major and trace element geochemistry from these rocks and measure their iron isotope compositions to investigate the potential role of fractional crystallization during melt evolution. We observe a large range of δ56Fe that defines a significant inverse curvilinear correlation with bulk rock MgO/FeOT. These data confirm that δ56Fe in the melt increases as fractional crystallization proceeds but, contrary to expectation, δ56Fe continues to increase even when oxides begin to crystallize. We conclude that iron isotope fractionation through fractional crystallization during the evolution of mid-ocean ridge basalts from abyssal peridotites reconciles the disparity in isotopic compositions between these two lithologies.

The hafnium paradox and the role of garnet in the source of mid-ocean-ridge basalts

Nature ◽  
1989 ◽  
Vol 342 (6248) ◽  
pp. 420-422 ◽  
Author(s):  
Vincent J. M. Salters ◽  
Stanley R. Hart
Keyword(s):  
Mid Ocean Ridge ◽  
Ocean Ridge

scholarly journals Mantle heterogeneity in the source region of mid-ocean ridge basalts along the northern Central Indian Ridge (8°S-17°S)

2017 ◽  
Vol 18 (4) ◽  
pp. 1419-1434 ◽  
Author(s):  
Jonguk Kim ◽  
Sang-Joon Pak ◽  
Jai-Woon Moon ◽  
Sang-Mook Lee ◽  
Jihye Oh ◽  
...  
Keyword(s):  
Source Region ◽  
Mantle Heterogeneity ◽  
Central Indian Ridge ◽  
Mid Ocean Ridge ◽  
Indian Ridge ◽  
Ocean Ridge

The petrology of the Harkerbreen Group, Ny Friesland, Svalbard: protoliths and tectonic significance

1990 ◽  
Vol 127 (2) ◽  
pp. 129-146 ◽  
Author(s):  
G. M. Manby
Keyword(s):  
Large Scale ◽  
Significant Proportion ◽  
Core Complex ◽  
Mid Ocean Ridge ◽  
Tectonic Significance ◽  
Discrimination Diagram ◽  
Early Palaeozoic ◽  
Back Arc ◽  
Ocean Ridge ◽  
Derivatives Of

AbstractThe late Precambrian–early Palaeozoic rocks of Ny Friesland, which have been subjected to Caledonian deformation and metamorphism, constitute part of the Eastern Province or Terrane of Svalbard. The Harkerbreen group and other divisions of the Stubendorffbreen supergroup form a high-grade and intensely deformed core complex to this terrane which is bounded to the west by the Billefjorden Fault Zone and to the east by a major north–south shear zone. The Stubendorffbreen rocks exhibit two gneissic foliations, one axial planar to a large scale, F1 fold nappe closing to the east and the other axial planar to kilometre-scale upright F2 folds subsidiary to the Atomfjella Arch. Metamorphism in the mid-amphibolite facies range coincided with generation of these folds, and F3.crenulation folding was accompanied by waning P–T conditions. A significant proportion of the gneisses within the Harkerbreen group display silica–major element covariation patterns consistent with their position in the granodiorite field on the AFM plot. Incompatible, immobile element ratios Zr/Ti v. Nb/Y indicate affinities with rhyolites to rhyodacites which is also suggested by their REE profiles. Normalized multi-element plots of the gneisses are similar to those of granites from attenuated within-plate settings such as Mull and Skaergaard. The amphibolites which were intruded in the D1–D2 interval appear to be derivatives of fractionated basalts. They plot across the calk-alkaline tholeiite boundary on the AFM diagram, and the calc-alkaline character of some of the amphibolites is further suggested by their Yb-normalized Ce-Ta abundances. Zr-Ti-Y and REE abundances would support their derivation from a related suite of fractionated basalt liquids. On the Zr/Y v. Zr discrimination diagram the amphibolites appear to have compositions transitional between Mid Ocean Ridge and Within-Plate basalts whilst the Zr-Nb-Ta plot indicates Volcanic Arc Basalt affinities. Th-Hf-Ta and multi-element plots, however, indicate a marginal to back-arc basin setting possibly above a mature subduction zone. The late Caledonian Chydenius granite is an adamellite with mixed within-plate and syn-orogenic characteristics typical of post-collisional granites.

Mantle Plume – Spreading Ridge Interaction: A Comparative Study of the Red Sea and Reykjanes Ridges

2020 ◽  
Author(s):  
Zachary Molitor ◽  
Oliver Jagoutz ◽  
Leigh Royden ◽  
Stephanie Brown ◽  
Guido Port ◽  
...  
Keyword(s):  
Melting Temperature ◽  
Red Sea ◽  
Dynamic Pressure ◽  
Spreading Ridge ◽  
Mantle Plumes ◽  
Reykjanes Ridge ◽  
Mid Ocean Ridge ◽  
Mantle Temperature ◽  
Ocean Ridge

<p>As a young, mid ocean ridge, the Red Sea is a unique natural laboratory for studying the processes that drive continental rifting and breakup. The role of hot spots, frequently attributed to mantle plumes, in triggering or driving breakup and their impact on crustal structure and topography is not well understood. We have found that the Red Sea ridge bears a resemblance to the Reykjanes ridge in terms of bathymetry, morphology, geophysical properties, basalt chemistry, and modelled melting temperature and pressure of primary basalts. The results of modelling basalt melting temperature call into question the role of mantle temperature on generating excess melt beneath the Red Sea and Reykjanes ridges. Within 300 kilometers of a hotspot center, determined by seismic tomography, mantle excess temperatures are as high as 300 degrees relative to an ambient mantle temperature of about 1300 C. Outside of this radius excess temperatures are not significant (less than 50 C), and unlikely to cause significant melting anomalies. It is likely that the southern Red Sea and northern Reykjanes ridge are directly affected by hot, buoyant upwelling from the Afar and Iceland mantle plumes, and the central Red Sea and southern Reykjanes ridge may be affected by dynamic pressure related to actively upwelling mantle around the mantle plumes.</p>

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